Cis-diene rubbers stabilized with dithiocarbamyl derivatives



United States Patent M 3,392,142 CIS-DIENE RUBBERS STABILIZED WIT DITHIOCARBAMYL DERIVATIVES Boris Nicholas Leyland, Gerald Scott, and Derek Williams, Manchester, England, assignors to Imperial Chemicals Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed Sept. 20, 1963, Ser. No. 310,496 Claims priority, application Great Britain, Sept. 24, 1962, 36,188/ 62 4 Claims. (Cl. 260-453) This invention relates to a method of preserving synthetic rubbers, particularly cis-rubbers.

It is well known that synthetic rubbers such as butadien'e/ styrene copolymers are susceptible to oxidation and must be protected by antioxidants. Numerous compounds have been proposed for this purpose. The recently developed cis-rubbers such as cis-polybutadiene and cis-polyisoprene similarly require stabilization and in the absence of suitable stabilisers the former changes on exposure to air especially at elevated temperatures to a gel of higher plasticity and the latter is degraded to a polymer of lower viscosity. However many of the antioxidants proposed for the non-stereospecific synthetic rubbers are not of value in the cis-rubbers.

We have now found that certain compounds containing a dithiocarbamyl group are efiective stabilizers for cisrubbers.

According to our invention therefore We provide a process for the preservation of synthetic cis-rubbers which comprises the addition to the cis-rubber of a dithiocarbamyl compound containing one or more groups of the formula:

wherein R and R each represent a hydrogen atom or an alkyl, aryl, cycloalkyl, substituted alkyl, or aralkyl radical, or R and R taken together, together with the nitrogen atom, represent a piperidino or morpholino radical, each of which groups is attached to an alkyl, substituted alkyl, alkylene or substituted alkylene group, a metal atom, an ammonium or alkyl substituted ammonium group, one or more sulphur atoms, or a group wherein R and R have the significance given hereinbefore.

As synthetic cis-rubbers there may be mentioned particularly cis-polybutadiene and cis-polyisoprene.

As dithiocarbamyl compounds useful in the process of our invention there may be mentioned in particular metal dialkyldithiocarbamates such as zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate or zinc dinonyldithiocarbamate which are especially valuable in the stabilization of cis-polybutadiene, alkylammoniumdialkyldithiocarbamates such as diethylammonium diethyldithiocarbamate, and dialkyldithiocarbamyl sulphides such as dinonyldithiocarbamyldisulphide which are especially valuable in the stabilisation of cis-polyisoprene.

Other dithiocarbamyl compounds which may be used in the process of our invention include diethyldithio- 3,392,142 Patented July 9, 1968 carbamylmonosulphide, and esters of dialkyldithiocarbamic acids such as 4-(diethylthiocarbamylthiomethyl)- 2 fi-dimethylphenol, 4- (diethylthiocarbamylthiomethyl 2: 6-di tert.-butylphenol and 2 6-bis (piperidinothiocarbamylthiomethyl)-4-rnethylphenol which may be obtained by interaction of the appropriate alkylphenol, formaldehyde, carbon bisulphide and amine. These compounds are of especial advantage since they have little effect on any vulcanisation process to which the rubber may be subjected. The dithiocarbamyl compound may be added to the cis-rubbers at any time before vulcanisation, but is preferably added as soon as possible after the formation of the cis-rubber and may with advantage be added to the polymerization reaction mixture in which the rubber is prepared.

The cis-rubber may be in any form, for example solid, dispersed, in emulsion, or in solution. Other antioxidants may also be present to assist the stabilising etfect, for example hindered phenols, such as 2:6-ditert.-butyl-pcresol, or bis-phenols normally used as rubber antioxidants, such as bis(2-hydroxy-3-tert.-butyl-5-methylphenyl)methane or bis(4-hydroxy-3-tert.-butyl-6-methylphenyl)methane or arylamines such as phenyl-fi-naphthylamine.

The dithiocarbamyl compound may be added in amount between 0.05 and 5% and preferably 0.1 and 1.0%, of the weight of rubber.

The rubber may also contain known adjuvants used in these compositions such as pigments, fillers, plasticisers, blowing agents, antiozonants, waxes, vulcanising agents, and vulcanisation accelerators and retarders.

The invention is illustrated but not limited by the following examples in which all parts and percentages are by weight unless otherwise stated:

EXAMPLE I 1 part of antioxidant is incorporated into 100 parts of cis-polybutadiene on a two roll mill. The polybutadiene is then sheeted off to a thickness of about 1 mm. and portions exposed to the air at 100 C. The plasticity is determined at intervals using a Wallace Plastometer in which the compressed height of a pellet of rubber is measured under a standard load at 100 C. The results obtained together with those of a control experiment on cis-polybutadiene to which no antioxidant was added are given in Table 1, and show the efiiciency of the antioxidants of our invention in hindering the formation of gel-like products of higher plasticity.

1 part of antioxidant is incorporated in 100 parts of cispolyisoprene on a mill with rolls at C. The polyisoprene is then sheeted oil? to a thickness of about 1 mm. and these sheets exposed in a suitable manner to an oxygen atmosphere at C. The times required to take up various amounts of oxygen are determined, the oxygen uptake being measured manometrically.

a a a The results obtained together with those of a control experiment on polyisoprene to which no antioxidant was added are given in Table II, and show clearly the longer time required by the stabilised polymer to absorb significant amounts of oxygen.

EXAMPLE 3 Antioxidants are tested under the conditions described in .Example 1. The results are summarized below in Table III.

4 EXAMPLE 5 Antioxidants are tested under the conditions described in Example 1. The results are summarized in Table V.

TABLE V Time of ageing in hours Antioxidant Wallace Plastieities Control (no antioxidant) 18 25 28 81 100 2-tert-butyl-6,diethylthioearbamoylthiomethyl-i-methylphenol 17 21 21 20 29 2-tert,butyl-S-piperidinothiocarbonylthiomethylA-methylphenol 17 21 21 27 30 2-tert-butyl-6-methyl-4pipeiidinothioearbonylthiomethylphenol 17 23 28 33 37 2zfi-di-tert-butyl-4piperidonothioearbonylthiomethylphenol 18 22 22 25 34 2:6-bis-(diethylthiocarbamoylthiomethyD-4-methylphenol 18 21 21 23 29 2:fi-bis-(morpholinothiocarbonylthiomethyl)-4-rnethylphenol 18 22 23 23 25 2-tert-butyl-tS-cyclohexylthioearbamoylthiomethy] Lmethylphenol 19 19 20 18 20 2:6-bis-(cyolohexylthiocarbamoylthiometnyl) -4-methylphenol 17 22 29 27 42 2 :6-bis- (n-butylthioearb amoylthiomethyl) -4-methylphenol 18 22 21 20 23 TABLE 111 Time of ageing at 100 C. in hours Antioxidant Wallace Plasticities N o antioxidant 20 75 100 Lead di-n-butyldithioearbamate 19 52 79 98 Zinc di-n-butyldithiocarbamate- 19 19 22 25 41 47 55 Antimony-di-n-butyldithiocarbarnate 20 19 23 23 32 36 36 Zinc N:N-pentamethylenedithiocarbamata 20 19 23 2a 41 38 4'1 Zine-N-ethyl-N-phenyldithiocarbamate 19 19 26 35 86 100 Bismuth diethyldithiocarbamate 19 18 20 21 21 24 Nickel diethyldithioearbamate I 19 12 4O 13 72 100 Sodium di-iso-propyldithiocarbamate 19 20 61 2 100 Potassiumbenzoylaminodithiocarbamate 19 19 a4 62 100 Antimony diethyldithiocarbamate 20 20 30 43 4-(diethylthiocarbamoylthiomethyl)2:6-dimethylphenoL 21 33 54 100 I 2-tert-hutyl-4-diethylthiocarbarnoyl-thiornethyl-5- methylphenol 21 18 25 100 2:fi-di-tert-buty1-4-diethylthiocarbamoylthiomethylphenoL 20 19 24 38 100 2-tert-butyl-4-diethy1thioearbamoylthiomethyl-fi-methylphenol 20 22 30 41 54 100 2:fi-bis-(piperidinothiocarbonylthiornethyl)-4-methy1phenol 21 19 25 2a 34 89 EPLAMPLE 4 We claim:

Antioxidants are tested under the conditions described in Example 2 and give the results summarized in Table IV.

TABLE IV (Percent) Oxygen Uptake Antioxidant 0.5 1.0 1.5 2.0

Time to absorb oxygen in hours Control 40 44 46 48 Zinc dibutyldithiocarbamate 242 248 250 Antimonydibutyldithiocarbamate. 379 385 388 Zinc-N-ethyl-N-phenyldithio-carbamate Bismuthdiethyldithioearbamate. Antimonydiethyldithio carbamate. Potassiumbenzoylaminodiethyldithiocarb amate 4(diethylthiocarbamoylthiomethyl) 2,6-dimetl1- yl nh an M 2-tert-butyl-4-dlixethylthiocarbamoylthiomethyl-5-methylp enol 2:fi-di-tert-butyl-4-diethyltbioearbamoylthiophenol 23 51 77 1. A composition of matter which comprises synthetic cis-diene rubber containing a stabilizing amount of an ester of a dialkyldithiocarbamic acid selected from the group consisting of 4-diethylthiocarbarnoylthiomethyl-Z,6-dimethylphen0l;

2 6-di-tert.-butyl-4-diethylthiocarbamoylthiornethylphenol;

2 6-bis (piperidinothiocarbonylthiomethyl -4-methylphenol;

2-tert.-butyl-4-diethylthiocarbamoylthiomethyl-S-methylphenol;

2-tert.-butyl-4-diethylthiocarbamoylthiomethyl-6-methylphenOl;

2-tert.-butyl-6-diethylthiocarbamoylthiomethyl-4-rnethylphenol;

220 60 Z-terL-butyl-6-piperidinothiocarbonylthiomethyl-4-methylphenol;

2-tert.-butyl-6-methyl-4-piperidinothi0carbonylthiomethylphenol;

2 6-di-tert.-butyl-4-piperidinothiocarbonylthiomethylphenol;

2 6-bis diethylthiocarbamoylthiomethyl -4-methylphenol;

2: 6bis(morpholinothiocarbonylthiomethyl) -4-methylphenol;

2-n-butylthiocarb amoylthiomethyl-4-methylphen0l;

2-tert.-butyl-6-cyclohexylthiocarbamoylthiomethyl-4- methylphenol 2 6-bis cyelohexylthiocarb amoylthiomethyl -4-methylphenol; and

2 6-bis(n-butylthiocarbamoylthiomethyl -4-methylphenol.

2. The composition of matter as claimed in claim 1 wherein the said ester of dialkyldithiocarbamic acid is present in an amount of about 0.05 to 5% by weight of said rubber.

3. The composition of matter as claimed in claim 2 wherein the said ester of dialkyldithiocarbamic acid is present in an amount of about 0.1 to about 1.0% by weight of said rubber.

4. The composition of matter as claimed in claim 1 which additionally includes an efiective amount of an antioxidant selected from the group consisting of 2:6-ditert. butyl p cresol, bis(2 hydroxy 3 tert. butyl- 5 methylphenyl)methane, bis(4 hydroxy 3 tert.- buty1-6-methylphenyl)methane and phenyl-fl-naphthylamine.

References Cited UNITED STATES PATENTS 2,375,042 5/1945 Semon 26045.9

6 2,789,962 4/1953 Groff et a1 26045.75 2,735,833 2/1956 Stanton et al. 260-45.9 2,974,082 3/1961 Collins 260-455 3,209,001 9/1965 Csendes 260-458 FOREIGN PATENTS 802,018 9/1958 Great Britain. 1,278,583 10/1961 France.

955,078 4/ 1964 Great Britain.

OTHER REFERENCES Industrial and Engineering Chemistry, Extrusion Plasticity of a Butadiene Acrylonitrile Rubber, by A. Campbell and P. Tryon, January 1953, vol. 45, No. 1,

DONALD E. CZAJA, Primary Examiner.

LEON J. BERCOVITZ, Examiner.

V. P. HOKE, Assistant Examiner. 

1. A COMPOSITION OF MATTER WHICH COMPRISES SYNTHETIC CIS-DIENE RUBBER CONTAINING A STABILIZING AMOUNT OF AN ESTER OF A DIALKYLDITHIOCARBAMIC ACID SELECTED FROM THE GROUP CONSISTING OF
 4. THE COMPOSITION OF MATTER AS CLAIMED IN CLAIM 1 WHICH ADDITINALLY INCLUDES AN EFFECTIVE AMOUNT OF AN ANTIOXIDANT SELECTED FROM THE GROUP CONSISTING OF 2:6-DITERT.-BUTYL-P-CRESOL, BIS(2-HYDROXY-3-TERT.-BUTYL5-METHYLPHENYL)METHANE, BIX-HYDROXY-3-TERT.-BUTYL-6-METHYLPHENYL)METHANE AND PHENYL-B-NAPHTHYLAMINE. 